Réponse :
1. Développer les expressions suivantes.
A = 3x (6x – 8) = 18x² - 24x
B = (x + 8) (– 6x + 7) = -6x² + 7x - 48x + 56 = -6x² - 41x + 56
C = (5x – 4) (2 – 3x) – (7 – x²) = 10x - 15x² - 8 + 12x - 7 + x² = -14x² + 22x - 15 D = (5x – 7)² = (5x-7)(5x-7) = 25x² - 35x - 35x + 49 = 25x² - 70x + 49
E = (3x + 2) (3x – 2) = 9x² - 6x + 6x - 4 = 9x² - 4
2. Factoriser les expressions suivantes.
A = 20x + 25 = 5(4x+5)
B = – 36x² + 11x = x(-36 + 11)
C = 18x² – 3x = 3x(6x-1)
D = (5x + 7) (2x – 11) + (–3x – 8) (5x + 7) = (5x+7)[(2x-11)+(-3x-8)] = (5x+7)(-x-19)
E = 4x² + 28x + 49 = (2x+7)(2x+7) = (2x+7)²
F = 16x² – 81 = (4x-9)(4x+9)
Explications étape par étape :
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Réponse :
1. Développer les expressions suivantes.
A = 3x (6x – 8) = 18x² - 24x
B = (x + 8) (– 6x + 7) = -6x² + 7x - 48x + 56 = -6x² - 41x + 56
C = (5x – 4) (2 – 3x) – (7 – x²) = 10x - 15x² - 8 + 12x - 7 + x² = -14x² + 22x - 15 D = (5x – 7)² = (5x-7)(5x-7) = 25x² - 35x - 35x + 49 = 25x² - 70x + 49
E = (3x + 2) (3x – 2) = 9x² - 6x + 6x - 4 = 9x² - 4
2. Factoriser les expressions suivantes.
A = 20x + 25 = 5(4x+5)
B = – 36x² + 11x = x(-36 + 11)
C = 18x² – 3x = 3x(6x-1)
D = (5x + 7) (2x – 11) + (–3x – 8) (5x + 7) = (5x+7)[(2x-11)+(-3x-8)] = (5x+7)(-x-19)
E = 4x² + 28x + 49 = (2x+7)(2x+7) = (2x+7)²
F = 16x² – 81 = (4x-9)(4x+9)
Explications étape par étape :